This invention relates in general to data communications within a wireless local area network (WLAN) and, in particular, to a WLAN using available TV white space spectrum and Long Term Evolution (LTE) system architecture for data communications.
Data communication within WLANs is now generally accomplished using WiFi implemented using one of the IEEE 802.11 standards. The 802.11b and 802.11g standards are designed to operate in the 2.4 GHz band using Direct Sequence Spread Spectrum (DSSS) technology. The 802.11n standard is designed to operate in the 2.4 GHz or the 5 GHz bands.
While WiFi works well, the high frequency signals do not readily penetrate obstructions, so a high transmit power must be used. This has raised health concerns that remain unaddressed. Furthermore, the wireless distribution of new data-intensive services such as High Definition Television (HDTV) and multimedia communications signals can undesirably degrade WLAN performance; and, the quality of service (QoS) of the HDTV or multimedia signals can be adversely affected if the WLAN is simultaneously used for the delivery of other data intensive services, such as internet access.
A radio standard called Long Term Evolution (LTE) has been developed by the 3rd Generation Partnership Project (3GPP). The goals of LTE are the provision of an all Internet Protocol (IP) packet network with faster download and upload speeds and reduced latency.
FIG. 1 is a schematic diagram of an LTE generic downlink radio frame structure 100. Each downlink radio frame 100 includes twenty time slots 102 numbered from 0 to 19 having a duration of 0.5 ms each. Two adjacent time slots make up a subframe 104 having a duration of 1 ms. Each downlink frame 100 has a duration of 10 ms.
FIG. 2 is a schematic diagram of the structure of each LTE downlink time slot 102. The smallest time-frequency unit for downlink transmission is called a resource element 106, which constitutes one symbol on one sub-carrier. A group of 12 sub-carriers that are contiguous in frequency within the time slot 102 form a resource block 108. When the downlink frame structure 100 uses a normal cyclic prefix, the 12 contiguous sub-carriers in the resource block 108 have a sub-carrier spacing of 15 kHz with 7 consecutive symbols in each downlink time slot 102. The cyclic prefix is appended to each symbol as a guard interval. The symbol plus the cyclic prefix form the resource element 106. Consequently, the resource block 108 has 84 resource elements (12 sub-carriers×7 symbols) corresponding to one time slot 102 in the time domain and 180 kHz (12 sub-carriers×15 kHz spacing) in the frequency domain. The size of a resource block 108 is the same for all bandwidths. In the frequency domain, the number of available sub-carriers can range from 76 sub-carriers when the transmission bandwidth is 1.25 MHz, to 1201 sub-carriers when the transmission bandwidth is 20 MHz.
LTE has been designed to be very robust and supports data rates of up to 100+ Mbps on the downlink and 50+ Mbps on the uplink. Although it is optimized for user equipment travel speeds of 0-15 km/h, travel speeds of 15-120 km/h are supported with high efficiency. To accomplish this level of performance, “reference” or “pilot” symbols are inserted in predetermined resource element positions within each transmitted resource block 108. The pilot symbols are used by receiver channel estimation algorithms to correct for received signal distortions.
FIG. 3 is a schematic diagram of some of the pilot symbols 120 transmitted in the LTE downlink frame 100, for a single antenna case. The pilot symbols 120 are transmitted at OFDM symbol positions 0 and 4 of each time slot 102.
In May of 2004, the Federal Communications Commission (FCC) approved a Notice of Proposed Rulemaking to allow a new generation of wireless devices to use vacant television frequencies (TV white spaces) on an unlicensed basis. These TV white spaces are frequency channels allocated for television broadcasting that will not be used in given geographic areas after Feb. 17, 2009. Specifically, the FCC will allow unlicensed operation in the spectrum used by TV channels 5 and 6 (76-88 MHz); 7 through 13 (174-213 MHz); 14 through 36 (470-608 MHz); and, 38 through 51 (614-698 MHz).
Many proposals exist for using the unlicensed TV white space spectrum. For example, it has been suggested that Wireless Regional Area Networks (WRANs) could be established to provide high-speed internet access to single family dwellings, multiple dwelling units and small businesses. The WRANs would operate using the IEEE 802.22 architecture over the TV white space spectrum with a fixed deployment and a larger coverage (25˜30 km range).
While these proposals have merit, they do not provide an efficient solution to the developing congestion in WLANs due to the emerging requirement to distribute HDTV signals wirelessly in a home environment. Furthermore, they do not provide interoperability with other systems or devices that use the LTE system architecture.
Therefore there exists a need for a local area network that uses the TV white space spectrum and the LTE system architecture.